Process for the production of fibers having polyvinyl chloride as the principal constituent and also containing polyvinyl alcohol



1963 I SEIZO OKAMURA ETAL. 3 9

PROCESS FOR THE PRODUCTION OF POLYVINYL FIBERS HAVING CHLORIDE AS THE PRINCIPAL CONSTITUENT AND ALSO CONTAINING POLYVINYL ALCOHOL Filed April 5, 1962 VINYLCHLORIDE POLYVINYLALCOHOL WATER CATALYST- EMULSIFIER EMULSION POLYMERIZATION POLYVINYLCHLORIDE EMULSION (P. V.C.)

POLYVINYLALCOHOL WATER (P.V.A) CONTAINING P.V.C. AND GRAFT CO- POLYMER OF VINYLCHLORIDE AND VINYLALCOHOL SPINNING SOLUTION I SPINNING I DRYING (wlmour TENSION) I HEAT 51' R ETCHING HEAT TREATING FORMALIZING (ACETALIZING) P.V.C. P.V.A FIBER ATTORNEY.

United States Patent PROCESS FOR THE PRODUCTION OF FIBERS HAVING PQLYVINYL CI-HJGRIDE AS Til-m PRIN- CIPAL CONSTETUENT AND ALSO C(BNTAINING PGLYVlNYL ALCGHOL Seizo Okamura, Sakyo-ku, Kyoto, Tadashi Muroi, Sugi= nami-ku, Tokyo, Hiroshi Asakura, Naka-gun, and Ippei Chimnra, Dai, Kamakura, dapan, assignors to Toyo Kagaku Co., Ltd, Dag Kamalrura, Japan, a corporation of Japan Filed Apr. 5, 1962, Ser. No. 185,222 12 Claims. (Cl. 18-54) The present invention relates to a process for the production of polyvinyl chloride (abbreviated as P.V.C. hereinafter) fibers containing at least 50% to 80%, by weight of P.V.C., and which have excellent heat resistivity and dyeability. Hereinafter, the term polyvinyl chloride is intended to mean a polymer of vinyl chloride, or copolymers in which the principal constituent is vinyl chloride.

The object of the present invention is to prepare stable spinning dopes, which do not precipitate when left for a long time, by polymerizing vinylchloride in a dispersing medium of polyvinyl alcohol *(hereinafter referred to as P.V.A.) in the presence of catalysts and emulsifiers to form an emulsion of P.V.C., in Which a part of the P.V.C. is grafted to P.V.A., and then adding a quantity of P.V.A. to such emulsion as a matrix.

Another object of the present invention is to improve the heat resistivity and dyeability of P.V.C. fiber by spinning the dope, consisting of a mixture of P.V.C. emulsion, having definite viscosity and definite particle size, and P.V.A., coagulating the spun fiber in a coagulating bath and then drying the coagulated fiber Without tension, in order to make it possible for subsequent dry-heat stretching and heat treatment and/ or formalization operations to greatly contribute to the improvement of heat resistivity and dyeability.

Heretofore, it has been well known that P.V.C. fiber is the least expensive to prepare of all of the synthetic fibers. But on the other hand it has the disadvantage that its heat resistivity and dyeability are inferior to that of other synthetic fibers. It is also known that attempts have been made to improve the properties of P.V.A. fibers by spinning a solution of P.V.A. and an emulsion of P.V.C. and then treating the spun and coagulated fiber by methods similar to those employed in the case of Vinylon (Trade name of P.V.A. fiber).

In all of these cases, however, attempts were made to improve the properties of P.V.A. fibers, therefore the principal constituent of these fibers were P.V.A., and the P.V.C. content was usually 20-30% and never exceeded 50%.

An increase of the P.V.C. content normally causes deterioration of the stretching and other properties of the fiber and, in fact, it is reported that spinning of such fiber is favorably performed, only if the content of P.V.C. in the fiber is less than 20-25%. Further, the stretching treatment after spinning becomes difiicult, when the content of P.V.C. is greater than the above value, and the tensile strength of the product decreases as the content of P.V.C. increases. Accordingly no attempt had been made to prepare synthetic fibers containing a large quantity of P.V.C.

The inventors have overcome the above mentioned difiiculties, and obtained P.V.C. fibers having improved heat resistivity and dyeability with a P.V.C. content as much as 50'80%, by polymerizing vinylchloride in a dispersing medium formed of an aqueous solution of P.V.A., to form an emulsion of P.V.C. having a viscosity less than 200 cp. and particle size less than 500A and the emulsion thus formed has P.V.A. added thereto to form a spinning dope.

This spinning dope is spun into fibers in a coagulating bath, and the coagulated fiber is dried Without tension. Then the dried fiber is subjected to dry-heat stretching at a temperature between C. and 230 C., and thereafter subjected either to heat treatment at a temperature between 180 C. and 230 C. or to formalization, or to both heat treatment and formalization successively.

The drawing is a flow sheet showing steps employed in preparing polyvinyl chloride fibers in accordance with a process embodying this invention.

Various investigations concerning the process embodying the present invention will now be explained in detail.

P.V.C. is a hydrophobic polymer Whereas P.V.A. is a hydrophilic one. Accordingly, it has been considered impossible to mix both polymers. Therefore, fiber consisting of both polymers does not possess good properties, and in fact it is considered difficult to spin the fiber from a spinning dope of a mixture of P.V.A. and P.V.C. contain ing more than 25% of P.V.C.

In accordance with the present invention, P.V.C. is made hydrophilic, by polymerizing vinylchloride in a dispersing medium, in the presence of catalysts and emulsifiers. The dispersing medium for this emulsion polymerization consists of an aqueous solution of P.V.A., so that a part of the P.V.C. is grafted to P.V.A., and thereby made hydro ph-ili'c.

Accordingly the P.V.C. emulsion may be added to a desired proportion of aqueous solution of P.V.A. as matrix to form a quite stable spinning dope, which does not precipitate when left for a long time. Therefore, it is easy to spin a fiber from this spinning dope, and it is possible to increase the content of P.V.C. up to 50-80%.

Table I, shows the relation between the concentration of P.V.A. in the dispersing medium and the rate of grafted P.V.C. to P.V.A., when polymerizing vinylchloride in a dispersing medium of P.V.A. at the temperature of 60 C., in the presence of potassium persulfate as the catalyst. Such catalyst being present in an amount of 2% of the vinylchlonide.

Nora-The quantity of graft polymer of P.V.C. to P.V.A. is measured by weighing the undissolved residue left after refluxing the product in Soxhlets extractor with hot water at 100 C. for 24 hours, and subsequently with tetrahydrofuran at 65 C. for 24 hours.

Next, a comparison was made of the properties of a product obtained from the P.V.C. emulsion produced by emulsion polymerization in P.V.A. solution and of a prodnot produced without P.V.A.

The same quantity of P.V.A. is added to both products as matrix and two films are prepared therefrom. The one prepared from the former product is transparent, whereas the film prepared from the latter is not transparent due to the deposition of P.V.C. particles which is perceptible with the naked eye.

In Table II, the tensile strength and elongation of both It is seen from the above that the products prepared in the dispersing medium of aqueous solution of P.V.A. become hydrophilic and have good afiinity with P.V.A. added as matrix and are mixed intimately with the matrix.

The mechanism of emulsion polymerization of P.V.C. in the dispersing medium of aqueous solution of P.V.A. was investigated under various conditions and the following facts were confirmed. When the degree of polymerization of P.V.A. is high, the stability of the emulsion increases as the concentration of P.V.A. decreases, and as the degree of polymerization of P.V.A. decreases, the stability increases as the concentration of P.V.A. increases.

Further, when the concentration of vinylchloride is kept constant, the degree of polymerization of P.V.C. decreases as the concentration of P.V.A. increases. Increasing the quantity of catalyst and the reaction temperature cause lowering of the degree of polymerization of P.V.C. Thus, it is possible to prepare emulsions for the spinning dope which contain P.V.C. and P.V.A. in any desired ratio.

In practice, it is important to determine the optimum range of P.V.C. concentration and viscosity of the spinning dope suitable for the spinning operation. As far as the concentration of P.V.C. in the dope is concerned, it is desirable to increase such concentration as far as possible, but as far as the viscosity of the dope is concerned, it is better to decrease it to some extent and, in any case, it is necessary to keep the viscosity constant for long periods of time. However, as the concentration of the spinning dope increases, its viscosity also gradually increases, and when the viscosity of the dope exceeds a certain limit, it can no longer be spun. Therefore, it is important to find suitable properties of the spinning dope.

Detailed investigations of the spinning dope composed of a mixture of P.V.C. emulsion obtained by the method mentioned above, and P.V.A. as matrix, indicate clearly that the polymerization yield of P.V.C. emulsion, viscosity and particle size of the emulsion, particularly particle size of the emulsion, greatly affect the viscosity of the spinning dope, and accordingly also the properties of the fiber to be produced.

For example, 0.4 part of catalyst and 6.0 parts of emulsifier were added to a mixture of 300 parts of aqueous solution containing 2.6% of P.V.A. and 230 parts of vinylchloride.

The mixture was subjected to polymerization and various kinds of emulsions were prepared by changing the time of polymerization. The properties of polymerized emulsions thus obtained are shown in Table 1H.

TABLE III Polymeri- Viscosity Quantity Particle zation of the of the size, A. yield, emulsion, polymer, percent cp. percent TABLE 'IV Viscosity of the Spinning Dope (in Seconds) Particle size (A) 240 350 500 570 Temperature C.)

These results show that the viscosity increases linearly as the panticle size increases.

In Table V, variation of the viscosity of the spinning dope with the passage of time after its preparation.

TABLE V Variation of Viscosity of the Spinning Dope With Time [Concentration 20% PVC: PVA=:50]

Particle Size Temp. Elapse of Elapse of Elapse of Elapse of Elapse of Elapse of (A.) C.) Time Time Time Time Time Time (hrs.) 2 (hrs.) 3 (hrs.) 4 (hrs.) 5 (hrs.) 6 (hrs.) 7

150 see 280 sec gelatinize. gelatinizegelatinize. gelatinize- 580 90 sec.... sec 200 see 250 secgelatinize,

70 60 as in ms ran 410 65 40 42 42 46 48 4Q invariable,

60 84 02 Inn 110 120 1'25 300 65 35 3") 35 35- invariable,

Norm-The numbers 01sec. 1n the table indicate the falling time for the steel ball through the column or liquid.

It is seen from the above results that when the particle size is larger than 500 A., a marked increase of viscosity is noticed with passage of time, and such increase appears even at high temperatures (70 C.).

It was found experimentally that when using the spinning dope composed of particles having a size larger than 500 A., homogeneous spinning was impossible and fibers having the desired superior properties could not be obtained.

Thus, it has been concluded that the spinning dope composed of P.V.C. emulsion must have a viscosity less than 200 cp. and the particle size must be smaller than 500 A.

Having explained the preparation of spinning dope, consisting of P.V.C. emulsion mixed with P.V.A., capable of producing improved P.V.C. fiber, the spinning processes using the spinning dope will now be described. As mentioned above, it has been previously reported that the properties of fibers were deteriorated as the P.V.C. content increases. In the Work forming the 'basis for these reports, the fibers were spun in a way similar to that of Vinylon.

However, it has been found that deterioration of the properties of the fiber due to the increase of the content of P.V.C. may be avoided by spinning the spinning dope, prepared by the above method, in a coagulating bath, such as sodium sulfate, drying the coagulated fiber without tension as far as possible, and then subjecting the fiber to dry heat stretching at temperatures between 140 C. and 230 C. and to subsequent heat treatment at temperatures between 180 C. to 230 C. or to formalization or to both heat treatment and formalization successively.

By this method, P.V.C. fibers of good quality have been prepared. The steps of drying the coagulated fiber without tension is one of the key points in the process embodying the present invention, and distinguishes such process from that employed in Vinylon spinning in which the coagulated fiber is immediately stretched by guides or rollers while in the wet state. The fact that stretching of the fibers in the wet state strikingly affects the properties of the fibers will be shown in the following.

In Table VI, there are given examples of the properties of the fibers prepared from the fiber (content of P.V.C. is 50%) from the coagulating bath, which fibers are subjected to varying amounts of stretching in the wet state prior to being stretched in the dry state.

It is clear from the results of Table VI that when the fiber from the coagulating bath is initially subjected to stretching in the wet state, the stretching ratio in the dry state cannot be made large and accordingly the tenacity at maximum stretching ratio is decreased by the process of stretching in the Wet state, as compared with the first example wherein all stretching is eifected in the dry state, as in accordance with this invention.

In accordance with the present invention the fiber stretched in the dry state is subjected to heat treatment at 180 C.230 C. under tension or to formalization, or to both heat treatment and formalization successively.

Table VII indicates the tenacity of fibers stretched in TABLE VH P.V.C. content, percent 50 60 70 Tenacity, g./d 5.0 3. 5 2. 5

Next, the temperatures at which stretching process and heat treatment are performed will be considered.

Hitherto, the heat treatments for P.V.C. fiber have been performed at temperatures between C. and C.

In accordance with the present invention, however, it is necessary to perform the stretching in the dry state to a stretching ratio of 7 at high temperatures in the range of C.230 C., and then the fiber is subjected to heat treatment under tension at temperatures in the range of 180 C.-230 C. By this process, thermal properties of the fiber are markedly improved and the heat resistivity of the fiber is greatly increased. These improved prop erties are apparent in the results shown in Table VIII.

TABLE VIII Shrinkage of P.V.C. Fibres in Percent Method of measurement: A weight of gram per denier is hung at one end of the fiber and the fiber is heated at a rising rate of 1 C./rnin. with the displacement of the weight being measured by cathetometer.

The heat resistivity measured in the boiling water is rather poor for the fibers subjected to heat treatment un der tension as compared with that of the fibers subjected to formalization. Thus, fibers subjected to heat treatment under tension have a shrinkage as high as 3035%, but by formalization this value is decreased to as little as 23%.

Next, dyeability will be considered. Since the P.V.C. fiber prepared .by the present invention, consists of a graft polymer of P.V.C. and P.V.A. (graft efliciency is 10- 20%: graft efliciency the quantity of P.V.C. grafted to P.V.A.

total quantity of P.V.C. the P.V.C., which is hydrophobic, is made hydrophilic due to the introduction of OH groups by graft copolymerization to P.V.A. Therefore, the P.V.C. fiber is made dyeable by direct, acid and sulfur dyes, by means of the ordinary methods. Deeper and brighter colour is obtained by dyeing, because this fibre has no core-skin structure as Vinylon.

Specific illustrative examples of the process embodying the invention will now be given.

EXAMPLE 1 Emulsifier and catalyst (potassium persulfate) are mixed with 230 parts of vinylchloride, 2.6 parts of polyvinyl alcohol and 300 parts of water and then the mixture is polymerized at 45 C. in an autoclave. An emulsion of P.V.C. (whose particle size is smaller than 500 A.) is obtained. The emulsion thus obtained is mixed with such quantity of P.V.A. that the ratio of P.V.C. to P.V.A. in the mixture becomes 1:1 (the content of P.V.C.: 50%) and the mixture is then spun in a bath of sodium sulfate (400 g./l.) and dried in air without tension. After such drying, the fiber is stretched to 7 times of its original length at 200 C., and subjected to heat treatment for 3 minutes under tension at 230 C. Then it is formalized in a solution containing sulfuric acid, sodium sulfate and formaldehyde for 3 minutes at 70 C. The fiber thus obtained has the following properties.

As is seen from the above table, the P.V.C. fiber has good tensile properties, excellent heat resistivity and dyeability.

EXAMPLE 2 Emulsifier and catalyst (potassium persulfate) are mixed with 230 parts of vinylchlon'de, 2.6 parts of P.V.A. and 300 parts of water and then the mixture is polymerized at 45 C. in an autoclave, and an emulsion of P.V.C. (Whose particle size is smaller than 500 A.) is obtained. The emulsion thus obtained is mixed with such quantity of P.V.A. that the ratio of P.V.C. to P.V.A. in the mixture becomes 6:4 (the content of P.V.C.: 60%) and the mixture is then spun in a coagulating bath of sodium sulfate (400 g./l.) and dried in air without tension. The dried fiber is stretched to 6 times of its original length at 180 C. and formalized in a solution containing sulfuric acid, sodium sulfate, and formaldehyde. The fiber thus obtained has the following properties.

Denier, d. 1.4 Tenacity, g./d. 3.1 Elongation, percent 10.6 Softening point in dry air, C. 160-170 Dyeability Good As is seen from the above results, the P.V.C. fiber has good tensile properties and excellent heat resistivity and dyeability.

EXAMPLE 3 Emulsifier and catalyst (potassium persulfate) are mixed with 230 parts of vinylchloride, 2.6 parts of P.V.A. and 300 parts of water and then the mixture is polymerized at 45 C. in an autoclave, and an emulsion of P.V.C. is obtained (whose particle size is smaller than 500 A.). The emulsion thus obtained is mixed with such quantity of =P.V.A. that the ratio of P.V.C. versus P.V.A. becomes 7:3 (the content of P.V.C.: 70%) and the mixture is then spun in a coagulating bath containing sodium sulfate (400 g./l.) and the coagulated fiber is dried in air without tension. The dried fiber then is stretched to 4.5 times its original length at 160 C. and lastly it is subjected to heat treatment at 200 C. for one minute. The fiber thus obtained has the following properties.

Denier, d. 2.0 Tenacity, g./d. 2.4 Elongation, percent 12.0 Softening point, C.:

In water 90-95 In dry air 130-140 Dyeability Good 8 so as to be hydrophilic, said emulsion having a viscosity less than 200 cp. and a particle size less than 500 A., and additional polyvinyl alcohol mixed with said emulsion so that the proportion of polyvinyl chloride in said dope is from 50 to by weight.

2. A method of preparing a spinning dope comprising the steps of polymerizing vinylchloride in a dispersing medium of polyvinyl alcohol in the presence of catalysts and emulsifiers so as to obtain an emulsion of polyvinyl chloride having a viscosity less than 200 cp. and a particle size less than 500 A., and adding polyvinyl alcohol to said emulsion.

3. A method as in claim 2; wherein the amount of polyvinyl alcohol added to said emulsion is suflicient to result in a concentration of polyvinyl chloride in the spinning dope in the range between 50% and 80%, by weight.

4. A method as in claim 2; wherein said catalyst is potassium persulfate.

5. A process for the production of fibers containing a major proportion of polyvinyl chloride and a minor proportion of polyvinyl alcohol, comprising the steps of polymerizing vinyl chloride in a dispersing medium of polyvinyl alcohol in the presence of catalysts and emulsifiers in order to obtain an emulsion of polyvinyl chloride having a viscosity less than 200 cp. and a particle size less than 500 A., adding polyvinyl alcohol to said emulsion to provide a spinning dope, spinning said dope in a coagulating bath to obtain coagulated fibers, drying said coagulated fibers without tension, subjecting the dried fibers to dry-heat stretching at a temperature in the range between approximately C. and 230 C., and then heat-treating the stretched fibers under tension at a temperature in the range between approximately 180 C. and 230 C.

6. A process as in claim 5; wherein the heat-treated fibers are further formalized by being immersed in a formalization solution.

7. A process as in claim 6; wherein said formalization solution contains sulfuric acid, sodium sulfate and formaldehyde.

8. A process as in claim 5; wherein said coagulating bath is an aqueous solution of sodium sulfate.

9. A process as in claim 5; wherein the amount of polyvinyl alcohol added to said emulsion is sufficien-t to provide a concentration of 50 to 80%, by weight, of polyvinyl chloride in said spinning dope.

10. A process for the production of fibers containing a major proportion of polyvinyl chloride and a minor proportion of polyvinyl alcohol, comprising the steps of polymerizing vinyl chloride in a dispersing medium of polyvinyl alcohol in the presence of catalysts and emulsifiers in order to obtain an emulsion of poiyvinyl chloride having a viscosity less than 200 cp. and a particle size less than 500 A., adding polyvinyl alcohol to said emulsion to provide a spinning dope, spinning said dope in a coagulating bath to obtain coagulated fibers, drying said coagulated fibers without tension, subjecting the dried fibers to dry-heat stretching at a temperature in the range between approximately 140 C. and 230 C., and then formalizing the stretched fibers by immersing the latter in a formalization solution.

11. A process as in claim 10; wherein said formalization solution contains sulfuric acid, sodium sulfate and formaldehyde.

12. A process as in claim 10; wherein the amount of polyvinyl alcohol added to said emulsion is suflicient to provide a concentration of 50 to 80%, by Weight, of polyvinyl chloride in said spinning dope.

References Cited in the file of this patent UNITED STATES PATENTS 3,007,228 Matsubayashi et al Nov. 7, 196 1 

1. A SPINNIG DOPE CONSISTING OF AN EMULSION OF POLYVINYL CHLORIDE AT LEAST PARTIALLY GRAFTED TO POLYVINYL ALCOHOL SO AS TO BE HYDROPHILIC, SAID EMULSION HAVING A VISCOSITY LESS THAN 200 CP. AND A PARTICLE SIZE LESS THAN 500 A., 